The invention relates to a machine tool, in particular a machine for working with punches and dies parts formed from sheet material, comprising an essentially C-shaped frame made up of two parallel-connected, essentially C-shaped parts, the first of which is designed to absorb the reaction forces from forces exerted by tools placed between the arms of the C-shaped parts, while the second is designed to hold the tools in a desired position relative to each other.
Such a machine is known from German Offenlegungsschrift No. 19 20 749. Such machines are used for, for example, punching holes of varying sizes in material of sometimes considerable thickness. The forces exerted on the frame can be very great; often of the order of many thousands of newtons.
A problem which occurs in machine tools with C-shaped frames is that, due to the considerable forces which are exerted on the C-shaped frame, the frame tends to gape, i.e. the arms of the frame bend apart during the machining of a workpiece. The position of the tools in the bottom and top arm relative to each other cannot consequently be fully controlled. This leads to a loss of accuracy. In punching machines in particular this is undesirable. In punching machines the degree of gaping of the frame is one of the factors affecting the size of the clearance between punch and die. The greater the "gaping effect" the more the clearance deviates from the clearance corresponding to a particular sheet thickness, and the greater is the burr information.
An attempt to eliminate these disadvantages of conventional C-shaped frames was made by providing a C-shaped frame made up of two parts, one part absorbing the reaction forces exerted by the tools, and the other part having to hold the tool (for example, punch and die) as well as possible in their correct positions.
In old frames of this type the two frame parts were connected to each other, either by means of the bedplate (which in that case has to be made very heavy), or by means of the table of the machine. In these machines, however, the frame parts could not function independently of each other, so appreciable gaping took place.
An improvement was made over the German Offenlegungsschrift, in which the two C-shaped frame parts are connected by a press table, by connecting the two parts of the frame hingedly to each other of the machine couples were produced which tended to make both frame parts gape, so that the accuracy was not always optimum, particularly if very considerable forces were exerted.